However I choose not to kill them, because they can break quests.
For example if we kill Ysolda we can't finish the A night to remember, which is getting fixed in 1.5, but probably won't fix it if we already killed her.
Focus: Do you kill named NPC without having a quest for it? If so, why?
If you killed an NPC without knowing the consequence, did you learn about your mistake afterwards? If so, did you reload a previous save? What was your reaction when finding out this cost you a trophy/achivement?
Have you killed NPCs and now having reading this, do you regret that now?
Do you like the fact that the game will make some of these NPCs unkillable until the quest has been done? Is this another step towards the "no freedom and no consequence" type of we, the players, do NOT want it to be?